Scientific Forecaster Discussion
fxus63 kmpx 210918
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
418 am CDT Fri Sep 21 2018
Short term...(today and tonight)
issued at 418 am CDT Fri Sep 21 2018
The surface low that brought US the severe weather Thursday is now
up over Central Lake Superior with Minnesota and western WI firmly within
its cool cyclonic flow. Deepest moisture and steady light rain, per
infrared cloud top temperatures, has been up across nodak into
northwest Minnesota and we are not expecting it to make it into central Minnesota.
However, a moist boundary layer with steep lapse rates has been
enough to generate the occasional bout of drizzle across
western and central Minnesota, but this should end pretty quickly this
morning. With the cold advection, we have seen stratus envelop the
region, with winds at times gusting up to around 35 mph. These cloud
will stick with US through the morning, but a rapid clearing of
skies from northwest to southeast is expected during the afternoon.
Also during the afternoon, high pressure will be moving overhead, so
winds will be calming down this afternoon as well. Afternoon highs
will remain in the 50s, but for many, you slept through what will be
the high for today back at 1 am CDT (12am cst), so for msp, the
streak of days with a high of 60 or greater that started on may 12th
will continue on.
Tonight, clear skies with the high moving through will result in the
coolest night we have seen this fall. However, by 12z Saturday
morning, the high will be centered over Central Lake Michigan, which
will bring return flow and southerly winds to the entire area by
Saturday morning. In addition, when snow cover does not exist,
radiational cooling nights are maximized when you have dry soils.
After the last few days, our soils are rather saturated, so this
will likely contribute to keeping lows tonight a bit warmer than you
might otherwise think. Still, in central WI, we should see lows drop
off into the low to mid 30s, but with the uncertainties mentioned,
we held off on issuing a frost advisory on what looks like a
marginal and localized frost threat out around Rusk County in WI.
Long term...(saturday through thursday)
issued at 418 am CDT Fri Sep 21 2018
For the extended, we'll have beautiful weather this weekend and get
a chance to dry out before the next front brings a renewed chance
for showers and thunderstorms Monday and Monday night. The pattern
next week still looks to become highly amplified, with ridges
building on either coast of North America, with a trough down the
middle, keeping US cooler and unsettled.
This weekend will feature a strong shortwave working across the
northern rockies. This will excite a Lee cyclone in montanan, which
will kick off warm air advection across the plains. The primary baroclinic zone
will setup across the international border, so we'll have mainly
sunny skies both days, with highs Saturday in the 60s and mid 70s on
Sunday out in western Minnesota.
Surface cyclone that develops over the High Plains this weekend will
send a cold front across our area Monday/Monday night. There are
still timing differences with the front, with the GFS still running
about 6-12 hours faster than the European model (ecmwf). A line storms will likely
develop along the front. Shear and mid level lapse rates will be
more than sufficient to support a severe threat, but surface
dewpoints only around 60 will limit our instability potential and
likely limit the severe threat we see with this fropa. Given the
slower progression of the front, we still look to work one more nice
day out of Monday with highs well into the 70s before we cool down.
Next week, models continue to show the flow becoming highly
amplified with large ridges developing on the west and east coasts
of North America, with a deep trough in the middle for US. This will
help knock our highs back into the 50s and 60s with lows in the
30s and 40s, but will also be an active pattern. Both the GFS/European model (ecmwf)
show a fairly strong clipper type system moving across the upper MS
valley mid-week. The low looks to stay to our north, so best rain
chances will be across northern Minnesota, but we will probably see some
showers work across the area with the cold front Wednesday night
into Thursday, which is when some chance pops return. We'll see a
strong baroclinic zone develop behind this system for the end of
next week and where it sets up will determine where another
widespread rain event sets up for next weekend.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1108 PM CDT Thu Sep 20 2018
Convection has exited to the east to all that remains is low
stratus through late tomorrow morning. IFR-or-lower ceilings
expected for the overnight hours through daybreak then ceilings
will nudge up to MVFR before clouds scatter out with VFR
prevailing mid-to-late afternoon Onward. Winds will continue to
swing around to west and northwest overnight through tomorrow with speeds
generally around 15g25kt through the day tomorrow before settling
down close to 10kt tomorrow evening.
Kmsp...IFR ceilings to last through the Friday morning push then
ceilings likely to rise over 1700ft by midday. No additional
/Outlook for kmsp/
Sat...VFR. Wind SW 5-10 kts.
Sun...VFR. Wind southeast 5-10 kts.
Mon...mainly VFR. Chc MVFR/thunderstorms and rain late. Winds S 10-20 kts.